Systems and methods for controlling surge margin in the compressor section of a gas turbine engine

ABSTRACT

Systems and methods are disclosed for controlling surge margin in the compressor section of a gas turbine engine. Bypass ports on a first compressor section and second compressor section lead to a bypass conduit. An auxiliary turbine and discharge conduit are positioned in the bypass conduit. Fluid flow from the compressor sections into the bypass conduit via the bypass ports is controlled by bypass control valves.

BACKGROUND

In modern gas turbine engines, bleeding air from a later stage of acompressor is a common technique for controlling the surge margin in thecompressor. Since the compressor has already performed work on the air,this technique of bleeding air from a compressor trades efficiency forsurge margin. While bleeding air may be essential to maintaining surgemargin in a compressor, improvements are desired that would reduceand/or eliminate the efficiency penalty associated with bleeding air.

SUMMARY

According to some aspects of the present disclosure, a system isdisclosed for controlling surge margin in a compressor section of a gasturbine engine. The system comprises a first compressor section, asecond compressor section, a bypass conduit, first and second compressorsection bypass ports and bypass control valves, an auxiliary turbine,and a discharge conduit with a discharge control valve. The firstcompressor section comprises one or more compressor stages defining afirst compressor section flowpath and a first compressor sectiondischarge in fluid communication with the first compressor sectionflowpath. The first compressor section bypass port is positioned alongthe first compressor section and in fluid communication with the firstcompressor flowpath. The second compressor section comprises one or morecompressor stages defining a second compressor section flowpath and asecond compressor section discharge in fluid communication with thesecond compressor section flowpath. The second compressor sectionflowpath is in fluid communication with the first compressor sectionflowpath. The second compressor section bypass port is positioned alongthe second compressor section and in fluid communication with the secondcompressor section flowpath. The bypass conduit extends between thefirst compressor section bypass port and the second compressor sectionbypass port. The first compressor section bypass control valve ispositioned in the bypass conduit downstream of the first compressorsection bypass port. The second compressor section bypass control valveis positioned in the bypass conduit downstream of the second compressorsection bypass port. The auxiliary turbine is positioned in the bypassconduit between the first compressor section bypass control valve andthe second compressor section bypass control valve. The dischargeconduit is coupled to and in fluid communication with the bypass conduitbetween the auxiliary turbine and the second compressor section bypasscontrol valve. The discharge control valve is positioned in thedischarge conduit.

In some embodiments the auxiliary turbine drives a motor-generator. Insome embodiments the auxiliary turbine is an impulse turbine. In someembodiments the system further comprises a controller, the controller incommunication with the first compressor section bypass control valve,the second compressor section bypass control valve, and the dischargecontrol valve. In some embodiments the controller is further incommunication with the auxiliary turbine. In some embodiments thecontroller is configured to control a position of one or more of thefirst compressor section bypass control valve, the second compressorsection bypass control valve, and the discharge control valve tomaintain surge margin of one or both of the first compressor section andthe second compressor section at or above a predetermined level.

According to further aspects of the present disclosure method isdisclosed for controlling surge margin in a compressor section of a gasturbine engine. The method comprises operating a first compressorsection to increase the pressure of a fluid flowing therethrough, thefirst compressor section comprising one or more first compressor stagesdefining a first compressor section flowpath, a first compressor sectiondischarge in fluid communication with the first compressor sectionflowpath, and a first compressor section bypass port positioned alongthe first compressor section and in fluid communication with the firstcompressor section flowpath; discharging the fluid from the firstcompressor section and directing the fluid to a second compressorsection, the second compressor section comprising one or more secondcompressor stages defining a second compressor section flowpath in fluidcommunication with the first compressor section discharge, a secondcompressor section discharge in fluid communication with the secondcompressor section flowpath, and a second compressor section bypass portpositioned along the second compressor section and in fluidcommunication with the second compressor section flowpath; operating thesecond compressor section to increase the pressure of the fluid flowingtherethrough; diverting a portion of the fluid flowing through thesecond compressor section via the second compressor section bypass portto a bypass conduit; directing the diverted portion of fluid through anauxiliary turbine positioned in the bypass conduit; and directing thediverted portion of fluid in the bypass conduit into the fluid flowingthrough the first compressor section via the first compressor sectionbypass port.

In some embodiments the method further comprises discharging a portionof the diverted portion of fluid via a discharge conduit. In someembodiments the step of diverting a portion of the fluid flowing throughthe second compressor section via the second compressor section bypassport comprises opening a second compressor section bypass control valvepositioned in the bypass conduit. In some embodiments the step ofdiverting a portion of the fluid flowing through the second compressorsection via the second compressor section bypass port further comprisesthrottling the second compressor section bypass control valve to controlthe flow rate of diverted fluid.

In some embodiments the step of directing the diverted portion of fluidin the bypass conduit into the fluid flowing through the firstcompressor section comprises opening a first compressor section bypasscontrol valve positioned in the bypass conduit. In some embodiments thestep of directing the diverted portion of fluid in the bypass conduitinto the fluid flowing through the first compressor section furthercomprises throttling the first compressor section bypass control valveto control the flow rate of directed fluid. In some embodiments therotational speed of the auxiliary turbine is at least partly controlledby throttling the second compressor section bypass control valve. Insome embodiments the rotational speed of the auxiliary turbine is atleast partly controlled by throttling the first compressor sectionbypass control valve. In some embodiments the step of discharging aportion of the diverted portion of fluid via a discharge conduitcomprises opening a discharge control valve positioned in the dischargeconduit. In some embodiments the rotational speed of the auxiliaryturbine is at least partly controlled by throttling the dischargecontrol valve.

According to still further aspects of the present disclosure, a methodis disclosed for controlling surge margin in a compressor section of agas turbine engine. The method comprises operating a first compressorsection to increase the pressure of a fluid flowing therethrough, thefirst compressor section comprising one or more first compressor stagesdefining a first compressor section flowpath, a first compressor sectiondischarge in fluid communication with the first compressor sectionflowpath, and a first compressor section bypass port positioned alongthe first compressor section and in fluid communication with the firstcompressor section flowpath; discharging the fluid from the firstcompressor section and directing the fluid to a second compressorsection; diverting a portion of the fluid flowing through the firstcompressor section via the first compressor section bypass port to abypass conduit; and directing the diverted portion of fluid through anauxiliary turbine positioned in the bypass conduit.

In some embodiments the method further comprises discharging thediverted portion of fluid after flowing through the auxiliary turbinevia a discharge conduit. In some embodiments the step of diverting aportion of the fluid flowing through the first compressor sectioncomprises opening a first compressor section bypass control valvepositioned in the bypass conduit. In some embodiments the rotationalspeed of the auxiliary turbine is at least partly controlled bythrottling the first compressor section bypass control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will be apparent from elements of the figures, which areprovided for illustrative purposes.

FIG. 1 is a schematic view of a system for controlling surge margin in acompressor section in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a schematic view of a system for controlling surge margin in acompressor section in accordance with some embodiments of the presentdisclosure.

FIG. 3 is a schematic view of the operation a system for controllingsurge margin in a compressor section in accordance with some embodimentsof the present disclosure.

FIG. 4 is a schematic view of the operation a system for controllingsurge margin in a compressor section in accordance with some embodimentsof the present disclosure.

FIG. 5 is a schematic view of the operation a system for controllingsurge margin in a compressor section in accordance with some embodimentsof the present disclosure.

FIG. 6 is a flow diagram of a method of controlling surge margin in acompressor section in accordance with some embodiments of the presentdisclosure.

FIG. 7 is a flow diagram of a method of controlling surge margin in acompressor section in accordance with some embodiments of the presentdisclosure.

FIG. 8 is a flow diagram of a method of controlling surge margin in acompressor section in accordance with some embodiments of the presentdisclosure.

The present application discloses illustrative (i.e., example)embodiments. The claimed inventions are not limited to the illustrativeembodiments. Therefore, many implementations of the claims will bedifferent than the illustrative embodiments. Various modifications canbe made to the claimed inventions without departing from the spirit andscope of the disclosure. The claims are intended to coverimplementations with such modifications.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments in the drawings and specific language will be used todescribe the same.

The present disclosure is directed to systems and methods forcontrolling and improving surge margin in the compressor section of agas turbine engine while reducing efficiency losses associated withbleeding air from the compressor section. The present disclosureprovides a system for using air bled from the compressor section torotate an auxiliary turbine and therefore recover work performed by thesystem and improve system efficiency as compared to a system that merelybleeds air from the compressor section. The present disclosureadditionally presents methods of operating a compressor section andbypass system to control and improve surge margins the compressorsection.

A system 100 for controlling surge margin in the compressor section 101of a gas turbine engine is schematically presented in FIGS. 1 and 2. Thesystem 100 may comprise a compressor section 101 and a bypass section102.

The compressor section 101 may comprise a compressor section inlet 107,a first compressor section 103, a second compressor section 105, and acompressor section outlet 109. The first compressor section 103 maycomprise one or more first compressor stages 111 and a first compressorsection discharge 113. The first compressor section stages 111 define afirst compressor section flowpath 112. The first compressor sectiondischarge 113 is in fluid communication with the first compressorsection flowpath 112.

The second compressor section 105 may comprise one or more secondcompressor stages 115 and a second compressor section discharge 117. Thesecond compressor section stages 115 define a second compressor sectionflowpath 114. The second compressor section discharge 117 is in fluidcommunication with the second compressor section flowpath 114. Thesecond compressor section flowpath 114 is in fluid communication withthe first compressor section flowpath 112.

During operation, the compressor section 101 accepts fluid through thecompressor section inlet 107 and rotating bladed rotors of the first andsecond compressor section stages 111, 115 increase the pressure of thefluid before the fluid is discharged via the compressor section outlet109. During operation, the second compressor section 105 typicallyreceives fluid discharged from the first compressor section 103. Fluiddischarged at the compressor section outlet 109 may be sent to acombustion chamber of the gas turbine engine, or may be used inadditional applications requiring a pressurized fluid.

A bypass section 102 of system 100 may comprise a first compressorsection bypass port 125, a second compressor section bypass port 127, afirst compressor section bypass control valve 119, a second compressorsection bypass control valve 121, and a bypass conduit 123. In someembodiments, the bypass section 102 further comprises an auxiliaryturbine 129 positioned in the bypass conduit 123. In some embodiments,the bypass section 102 further comprises a discharge conduit 135 influid communication with at least a portion of the bypass conduit 123.

The first compressor section bypass port 125 may be positioned at anypoint along the first compressor section 103 and may further be in fluidcommunication with the first compressor section flowpath 112. The firstcompressor section bypass port 125 is used to divert fluid flow from thefirst compressor section flowpath 112. The first compressor bypass port125 may be positioned at any stage of the first compressor section 103or at the first compressor section discharge 113. Although schematicallydepicted as a single port 125, the first compressor section bypass port125 may be multiple ports.

Flow through the first compressor section bypass port 125 may becontrolled by a first compressor section bypass control valve 119. Thefirst compressor section bypass control valve 119 may be positionedadjacent the first compressor section bypass port 125 or downstream ofthe port 125. The first compressor section bypass control valve 119 maybe opened, shut, or throttled to control fluid flow through the firstcompressor section bypass port 125.

The second compressor section bypass port 127 may be positioned at anypoint along the second compressor section 105 and may further be influid communication with the second compressor section flowpath 114. Thesecond compressor section bypass port 127 is used to divert fluid flowfrom the second compressor section flowpath 114. The second compressorbypass port 127 may be positioned at any stage of the second compressorsection 105 or at the second compressor section discharge 117. Althoughschematically depicted as a single port 127, the second compressorsection bypass port 127 may be multiple ports.

Flow through the second compressor section bypass port 127 may becontrolled by a second compressor section bypass control valve 121. Thesecond compressor section bypass control valve 121 may be positionedadjacent the second compressor section bypass port 127 or downstream ofthe port 127. The second compressor section bypass control valve 121 maybe opened, shut, or throttled to control fluid flow through the secondcompressor section bypass port 127.

The bypass conduit 123 extends between the first compressor sectionbypass port 125 and the second compressor section bypass port 127. Thebypass conduit 123 is generally in fluid communication with thedownstream sides of the first compressor section bypass control valve119 and the second compressor section bypass control valve 121. When thefirst compressor section bypass control valve 119 is open, the bypassconduit 123 may be in fluid communication with the first compressorsection bypass port 125 and the first compressor section flowpath 112.When the second compressor section bypass control valve 121 is open, thebypass conduit 123 may be in fluid communication with the secondcompressor section bypass port 127 and the second compressor sectionflowpath 114.

An auxiliary turbine 129 may be positioned in and in fluid communicationwith the bypass conduit 123. The auxiliary turbine 129 may be positionedbetween the first compressor section bypass control valve 119 and thesecond compressor section bypass control valve 121. The auxiliaryturbine 129 may drive a motor-generator 131 via a shaft 133. Theauxiliary turbine 129 may be an impulse turbine. Shaft 133 may beparallel with a shaft and/or axis of rotation of the compressor section101 and/or the gas turbine engine, or may have a divergent axis ofrotation.

A discharge conduit 135 may extend from and be in fluid communicationwith the bypass conduit 123 at a position between the auxiliary turbine129 and the second compressor section bypass control valve 121. Thedischarge conduit 135 may direct fluid flow to an atmospheric dischargeor to another system. Fluid flow through the discharge conduit 135 iscontrolled by a discharge control valve 137 positioned in the dischargeconduit 135.

In some embodiments, an additional discharge conduit and dischargecontrol valve may be provided, extending from and in fluid communicationwith the bypass conduit 123 at a position between the auxiliary turbine129 and the first compressor section bypass control valve 119.

A controller 239 may communicate with and/or control various componentsof the system 100. As shown by the dashed lines of FIG. 2, thecontroller 239 may communicate with and control one or more of the firstcompressor section 103, the second compressor section 105, the firstcompressor section bypass control valve 119, the second compressorsection bypass control valve 121, the auxiliary turbine 129, themotor-generator 131, and the discharge control valve 137. By controllingthe position of the first compressor section bypass control valve 119,the second compressor section bypass control valve 121, and thedischarge control valve 137, the controller 239 may control fluid flowthrough the system 100. Further, the controller 239 may control therotational speed of the auxiliary turbine 129 by controlling theposition (i.e. open, shut, or throttled) of the control valves 119, 121,137. The controller 239 may also control the rotational speed of theauxiliary turbine 129 by modulating the operating parameters of themotor-generator 131 and/or by modulating the instantaneous torque.

By controlling the fluid flow through the bypass section 102, thecontroller 239 may control the surge margin of one or more of thecompressor section 101, the first compressor section 103, and the secondcompressor section 105. The controller 239 may be configured to controlthe surge margin to a predetermined level, for example to apredetermined level of 10% below the surge line of a compressor section101.

FIGS. 3, 4, and 5 of the present disclosure illustrate various operatingconfigurations of the disclosed system 100. During operation, the bypasssection 102 may be offline, with the first compressor section bypasscontrol valve 119 and the second compressor section bypass control valve121 shut. However, in order to control and/or improve surge margin ofthe compressor section 101, including of one or both of the firstcompressor section 103 and the second compressor section 105, the firstcompressor section bypass control valve 119, the second compressorsection bypass control valve 121, and discharge control valve 137 may beoperated to control flow through the bypass section 102. Fluid flow inFIGS. 3, 4, and 4 is illustrated with arrows.

In the configuration shown in FIG. 3, the system 100 is configured tobleed air from the first compressor section 103. This configuration maybe particularly advantageous when used during low speed operations ofthe compressor section 101 and/or gas turbine engine, and may bereferred to as a boosted low speed operation. In standard low speedand/or low flow operating conditions for the compressor section 101, ableed port may provide for bleeding a portion of fluid flow toatmosphere. However, due to the low flow condition, there is relativelylittle bleed flow and thus the influence on surge margin is minimal. Bycontrast, in the configuration of FIG. 3 the auxiliary turbine 129 mayserve as an ejector for the first compressor section 103, thusincreasing bleed flow and improving the surge margin for the firstcompressor section 103, the compressor section 101, and/or the gasturbine engine. The auxiliary turbine 129 may be driven in theconfiguration shown in FIG. 3 by the motor-generator 131 such that theauxiliary turbine 129 is operating in a pump/compressor mode to increasebleed flow from the first compressor section 103.

As shown in FIG. 3, in some embodiments the system 100 may be operatedwith the first compressor section bypass control valve 119 in an open orthrottled open position, the second compressor section bypass controlvalve 121 in a shut position, and the discharge control valve 137 in anopen or throttled open position. The controller 239 may adjust theposition of the first compressor section bypass control valve 119 and/orthe discharge control valve 137 to adjust the flow rate of fluid throughthe bypass section 102.

In this configuration, fluid is admitted to the first compressor section103 via the compressor section inlet 107. The first compressor stages111 increase the pressure of the fluid and discharge the fluid to thesecond compressor section 105. A portion of the fluid is bled throughthe first compressor section bypass port 125 and enters the bypassconduit 123. This diverted or bled fluid operates the auxiliary turbine129, which in turn runs the motor-generator 131 via the shaft 133. Thediverted fluid exits the auxiliary turbine 129 and is discharged via thedischarge conduit 135. Throttling of the first compressor section bypasscontrol valve 119 and/or the discharge control valve 137 may adjust therotational speed of the auxiliary turbine and/or the power output of themotor-generator 131. With the second compressor section bypass controlvalve 121 in the shut position, no fluid flows through the secondcompressor section bypass port 127.

In the configuration shown in FIG. 4, the system 100 may be configuredto divert a portion of fluid from the second compressor section 105.This configuration may be referred to as recovered recirculation. Whilea typical recirculation in a compressor section of a gas turbine enginebleeds air at a downstream location and injects it at an upstreamlocation of the compressor section, the configuration disclosed in FIG.4 improves upon the thermodynamic efficiency of typical recirculation byusing the bleed fluid to power an auxiliary turbine 129 and potentiallythe motor-generator 131.

The system 100 may be operated with the first compressor section bypasscontrol valve 119 in an open or throttled open position, the secondcompressor section bypass control valve 121 in an open or throttledposition, and the discharge control valve 137 in a shut position. Thecontroller 239 may adjust the position of the first compressor sectionbypass control valve 119 and/or second compressor section bypass controlvalve 121 to adjust the flow rate of fluid through the bypass section102.

In this configuration, fluid is diverted from the second compressorsection flowpath 114 via the second compressor section bypass port 127and enters bypass conduit 123. The second compressor section bypasscontrol valve 121 is opened or throttled to control the flow rate offluid diverted from the second compressor section 105. The diverted orbled fluid operates the auxiliary turbine 129, which in turn runs themotor-generator 131 via the shaft 133. The diverted fluid exits theauxiliary turbine 129 and is directed or injected into the firstcompressor section 103 via the first compressor section bypass port 125.Throttling of the first compressor section bypass control valve 119and/or the second compressor section bypass control valve 121 may adjustthe rotational speed of the auxiliary turbine 129 and/or the poweroutput of the motor-generator 131. With the discharge control valve 137in the shut position, fluid is not discharged from the system 100.

In the configuration of FIG. 4, the temperature of fluid directed intothe first compressor section flowpath 112 may be controlled and/ormodulated by controlling the rotational speed of the auxiliary turbine129 and/or the power output of the motor-generator 131

The power output of the motor-generator 131 may be used in sub- orsupport systems of the gas turbine engine, may be diverted to othersystems (such as aircraft systems when the gas turbine engine ispowering an aircraft), and may be diverted to charge a battery orsimilar energy storage device.

In the configuration shown in FIG. 5, the system 100 may be configuredto divert a portion of fluid from the second compressor section 105,with some of the diverted portion used to drive the auxiliary turbine123 and some of the diverted portion discharged from the system 100.This configuration may be referred to as dynamic bleed. The system 100may be operated with the first compressor section bypass control valve119 in an open or throttled open position, the second compressor sectionbypass control valve 121 in an open or throttled position, and thedischarge control valve 137 in an open or throttled position. Thecontroller 239 may adjust the position of the first compressor sectionbypass control valve 119, second compressor section bypass control valve121, and/or discharge control valve 137 to adjust the flow rate of fluidthrough the bypass section 102.

In this configuration, fluid flow through the bypass section 102 may bedynamically adjusted and even changed directions based on desiredalterations to the surge margin of the compressor section 101 and/or thefirst compressor section 103 and second compressor section 105. Fluidflow may be diverted from the second compressor section 105, with aportion of the diverted flow discharged via the discharge conduit 135and a portion of the diverted flow directed to the first compressorsection 103 and used to operate the auxiliary turbine 129. While arelatively large fraction of air may be bled from through the secondcompressor section bypass control valve 121, some portion of the bledair may be used both to drive the auxiliary turbine 123 and to favorablychange the aerodynamic matching between the compressor sections 103,105. Fluid flow may be dynamically controlled and adjusted by thecontroller 239 and the positioning of one or more of control valves 119,121, and 137.

In some embodiments, not limited to the configuration shown in FIG. 5,the discharge conduit 135 may intersect the bypass section 102 betweenthe first compressor section bypass control valve 119 and the auxiliaryturbine 123. In the configuration shown in FIG. 5, positioning thedischarge conduit 135 between the first compressor section bypasscontrol valve 119 and the auxiliary turbine 123 may allow for drivingthe auxiliary turbine 123 with a higher differential pressure than theplacement of the discharge conduit 135 shown in FIG. 5.

The present disclosure additionally provides methods of controllingsurge margin in a compressor section 101 of a gas turbine engine.Examples of such methods are presented in the flow diagrams of FIGS. 6,7, and 8.

A method 600 of controlling surge margin in a compressor section 101 ofa gas turbine engine is presented in the flow diagram of FIG. 6. Method600 starts at Block 601. The steps of method 600, presented at Blocks601 through 619, may be performed in the order presented in FIG. 6 or inanother order. One or more steps of the method 600 may not be performed.Method 600 may be referred to as recovered recirculation and may in someembodiments correspond with the system 100 configuration presented atFIG. 4.

At Block 603 a first compressor section 103 may be operated to increasethe pressure of a fluid flowing through the first compressor sectionflowpath 112. The fluid may be discharged from the first compressorsection 103 at Block 605 and directed to a second compressor section105. At Block 607 the second compressor section 105 may be operated toincrease the pressure of the fluid flowing through the second compressorsection flowpath 114.

At Block 609 a portion of the fluid flowing through the secondcompressor section flowpath 114 may be diverted to the bypass conduit123 via the second compressor section bypass port 127. This step maycomprise opening a second compressor section bypass control valve 121positioned in the bypass conduit 123, and may further comprisethrottling the second compressor section bypass control valve 121 tocontrol the flow rate of fluid diverted from the second compressorsection 105.

At Block 611 the diverted fluid may be directed through an auxiliaryturbine 129 positioned in the bypass conduit 123.

At Block 613 the diverted fluid may be directed into the fluid flowingthrough the first compressor section 103 via the first compressorsection bypass port 125. This step may comprise opening a firstcompressor section bypass control valve 119 positioned in the bypassconduit 123, and may further comprise throttling the first compressorsection bypass control valve 119 to control the flow rate of fluiddirected into the first compressor section 103.

At Block 615 a portion of the diverted portion of fluid may bedischarged via a discharge conduit 135. The discharge may be initiatedand controlled by opening or throttling open a discharge control valve137 in the discharge conduit 135.

At Block 617 the rotational speed of the auxiliary turbine 129 may becontrolled. This step may be accomplished in a number of ways. Forexample, the rotational speed of the auxiliary turbine 129 may be atleast partly controlled by throttling one or more of the secondcompressor section bypass control valve 121, the first compressorsection bypass control valve 119, and/or the discharge control valve137.

Method 600 ends at Block 619.

A method 700 of controlling surge margin in a compressor section 101 ofa gas turbine engine is presented in the flow diagram of FIG. 7. Method700 starts at Block 702. The steps of method 700, presented at Blocks702 through 716, may be performed in the order presented in FIG. 7 or inanother order. One or more steps of the method 700 may not be performed.Method 700 may be referred to as boosted low speed operations and may insome embodiments correspond with the system 100 configuration presentedat FIG. 3.

At Block 704, a first compressor section 103 is operated to increase thepressure of a fluid flowing through the first compressor sectionflowpath 112. The fluid is discharged from the first compressor section103 at Block 706 and directed to a second compressor section 105.

At Block 708 a portion of the fluid flowing through the first compressorsection 103 is diverted via a first compressor section bypass port 125to a bypass conduit 123. The fluid may be diverted by opening orthrottling open a first compressor section bypass control valve 119positioned in the bypass conduit 123.

The diverted portion of fluid may be directed through an auxiliaryturbine 129 positioned in the bypass conduit 123 at Block 710. Dependingon the instantaneous needs of the thermodynamic cycle and the runningconditions of either or both of first compressor section 103 and secondcompressor section 105, the auxiliary turbine 123 may be used to eitherabsorb power from flow through the bypass section 102 (i.e. operated inturbine mode) or perform positive work on the flow through the bypasssection 102 in order to draw bleed flow from the first compressorsection 103 (i.e. operated in a pump/compressor/ejector mode).

At Block 712, the diverted portion of fluid may be discharged afterflowing through the auxiliary turbine 129 via a discharge conduit 135.

At Block 714 the rotational speed of the auxiliary turbine 129 may becontrolled, for example by throttling one or both of the firstcompressor section bypass control valve 119 and the discharge controlvalve 137.

Method 700 ends at Block 716.

A method 800 of controlling surge margin in a compressor section 101 ofa gas turbine engine is presented in the flow diagram of FIG. 8. Method800 starts at Block 801. The steps of method 800, presented at Blocks801 through 819, may be performed in the order presented in FIG. 8 or inanother order. One or more steps of the method 800 may not be performed.Method 800 may be referred to as dynamic bleed and may in someembodiments correspond with the system 100 configuration presented atFIG. 5.

At Block 803 a first compressor section 103 may be operated to increasethe pressure of a fluid flowing through the first compressor sectionflowpath 112. The fluid may be discharged from the first compressorsection 103 at Block 805 and directed to a second compressor section105. At Block 807 the second compressor section 105 may be operated toincrease the pressure of the fluid flowing through the second compressorsection flowpath 114.

At Block 809 a fluid flowpath may be formed for receiving bleed air fromthe second compressor section. This step may comprise opening a firstcompressor section bypass control valve 119 positioned in the bypassconduit 123, and may further comprise throttling the first compressorsection bypass control valve 119 to control the flow rate of fluiddiverted from the first compressor section 103.

At Block 811 a portion of the fluid flowing through the secondcompressor section flowpath 114 may be diverted to the bypass conduit123 via the second compressor section bypass port 127. This step maycomprise opening a second compressor section bypass control valve 121positioned in the bypass conduit 123, and may further comprisethrottling the second compressor section bypass control valve 121 tocontrol the flow rate of fluid diverted from the second compressorsection 105.

At Block 813 the fluid diverted from the second compressor section 105may be directed through an auxiliary turbine 129 positioned in thebypass conduit 123.

At Block 815 all or a portion of the fluid diverted from the secondcompressor section 105 may be discharged via a discharge conduit 135.This step may comprise opening and/or throttling open a dischargecontrol valve 137.

At Block 817 the rotational speed of the auxiliary turbine 129 may becontrolled. This step may be accomplished in a number of ways. Forexample, the rotational speed of the auxiliary turbine 129 may be atleast partly controlled by throttling one or more of the secondcompressor section bypass control valve 121, the first compressorsection bypass control valve 119, and/or the discharge control valve137.

Method 800 ends at Block 819.

The present disclosure provides numerous advantages over prior artcompressor bleed systems. The diverting or bleeding of fluid from thecompressor section may be used to maintain or improve the surge marginof the compressor section. The use of the diverted fluid to operate anauxiliary turbine and motor-generator reduces the efficiency losses ofthe system by recovering work from the fluid pressurized in thecompressor section. The disclosed bypass section also allows fordynamically controlling surge margin of the compressor section byadjusting the position of control valves to adjust and control fluidflow through the bypass section.

By increasing the ability and precision by which surge margin iscontrolled, the presently disclosed systems and methods also allowreducing the minimum surge margin at which a compressor section iscontrolled or operated. For example, in certain gas turbine engines itmay be common to establish a minimum surge margin of 15%. With thegreater control, flexibility, and precision afforded by the presentdisclosure, that minimum surge margin may be reduced to, for example,10% of even 8%. Such a reduction allows for a greater operating range ofthe compressor section while maintaining confidence that the compressorsection will avoid a surge condition.

Additional advantages of the disclosed systems and methods may includethat the use of the auxiliary turbine as an ejector may allow for areduction in the size and weight of the handling bleed apparatus. Theoperating line of the compressor and/or first compressor section andsecond compressor section may be modulated directly without incurringsevere thermodynamic losses or locating variable geometry in the hottestsection of the engine. The compressor may be designed at higherefficiency, owing to fewer compromises made in the name of maintainingadequate stability margin. Also, based on the presently disclosedsystems and methods the inter-stage matching of the compressor can bemodulated.

Still further, the auxiliary turbine and motor-generator may be used topower other systems on the platform (such as an aircraft) without acoaxial (and likely heavier) motor-generator. The reinjected fluid canbe used to re-energize low-momentum fluid in the flowpath, therebyimproving local aerodynamic performance and stability margin. Finally,handling bleed can be drawn from the compressor section without dumpingto atmosphere and generating high-intensity noise

Although examples are illustrated and described herein, embodiments arenevertheless not limited to the details shown, since variousmodifications and structural changes may be made therein by those ofordinary skill within the scope and range of equivalents of the claims.

What is claimed is:
 1. A method of controlling surge margin in acompressor section of a gas turbine engine, said method comprising:operating a first compressor section to increase a pressure of a fluidflowing therethrough, the first compressor section comprising one ormore first compressor stages defining a first compressor sectionflowpath, a first compressor section discharge in fluid communicationwith the first compressor section flowpath, and a first compressorsection bypass port positioned along the first compressor section and influid communication with the first compressor section flowpath;discharging at least a first portion of the fluid from the firstcompressor section and directing the first portion of the fluid to asecond compressor section, the second compressor section comprising oneor more second compressor stages defining a second compressor sectionflowpath in fluid communication with the first compressor sectiondischarge, a second compressor section discharge in fluid communicationwith the second compressor section flowpath, and a second compressorsection bypass port positioned along the second compressor section andin fluid communication with the second compressor section flowpath;operating the second compressor section to increase a pressure of thefluid flowing therethrough; opening a first compressor section bypasscontrol valve, in fluid communication with the first compressor sectionbypass port, and opening a second compressor section bypass controlvalve, in fluid communication with the second compressor section bypassport, diverting a second portion of the fluid flowing through the secondcompressor section via the second compressor section bypass port and viathe second compressor section bypass control valve to a bypass conduit,directing the diverted second portion of the fluid through an auxiliaryturbine positioned in the bypass conduit and directing the divertedsecond portion of the fluid in the bypass conduit into the fluid flowingthrough the first compressor section via the first compressor sectionbypass control valve and via the first compressor section bypass port;and closing the second compressor section bypass control valve,diverting, a third portion of the fluid flowing through the firstcompressor section via the first compressor section bypass port and viathe first compressor section bypass control valve to the bypass conduitand directing the diverted third portion of the fluid through theauxiliary turbine positioned in the bypass conduit.
 2. The method ofclaim 1 further comprising: when the second compressor section bypasscontrol valve is open, discharging a portion of the diverted secondportion of the fluid via a discharge conduit; and when the secondcompressor section bypass control valve is closed, discharging a portionof the diverted third portion of the fluid via the discharge conduit. 3.The method of claim 1 wherein the step of diverting the second portionof the fluid flowing through the second compressor section via thesecond compressor section bypass port further comprises throttling saidsecond compressor section bypass control valve to control the flow rateof the diverted second portion of the fluid.
 4. The method of claim 1wherein the step of directing the diverted second portion of the fluidin the bypass conduit into the fluid flowing through the firstcompressor section further comprises throttling said first compressorsection bypass control valve to control a flow rate of the divertedsecond portion of the fluid.
 5. The method of claim 1 wherein arotational speed of the auxiliary turbine is at least partly controlledby throttling said second compressor section bypass control valve. 6.The method of claim 1 wherein a rotational speed of the auxiliaryturbine is at least partly controlled by throttling said firstcompressor section bypass control valve.
 7. The method of claim 2wherein the step of discharging the portion of the diverted secondportion of the fluid via the discharge conduit or the step ofdischarging the portion of the diverted third portion of the fluid viathe discharge conduit comprises opening a discharge control valvepositioned in the discharge conduit.
 8. The method of claim 7 wherein arotational speed of the auxiliary turbine is at least partly controlledby throttling said discharge control valve.
 9. The method of claim 2,wherein the discharge conduit is located between the second compressorsection bypass port and the auxiliary turbine along the bypass conduit.10. The method of claim 1, wherein a motor-generator drives theauxiliary turbine in the second operating condition in a pump/compressormode to increase bleed flow from the first compressor section.
 11. Themethod of claim 1, wherein, when the second compressor section bypasscontrol valve is closed, the first and second compressor sectionsoperate at a first rotational speed, wherein, when the second compressorsection bypass control valve is open, the first and second compressorsections operate at a second rotational speed, and wherein the firstrotational speed is lower than the second rotational speed.
 12. A methodof controlling surge margin in a compressor section of a gas turbineengine, said method comprising: operating a first compressor section toincrease a pressure of a fluid flowing therethrough, the firstcompressor section comprising one or more first compressor stagesdefining a first compressor section flowpath, a first compressor sectiondischarge in fluid communication with the first compressor sectionflowpath, and a first compressor section bypass port positioned alongthe first compressor section and in fluid communication with the firstcompressor section flowpath; discharging the fluid from the firstcompressor section and directing the fluid to a second compressorsection having a second compressor section bypass port positioned alongthe second compressor section wherein the second compressor bypass portis in fluid communication with a second compressor section flowpath;opening a first compressor section bypass control valve in fluidcommunication with the first compressor section bypass port; closing asecond compressor section bypass control valve in fluid communicationwith the second compressor section bypass port; diverting a firstportion of the fluid flowing through the first compressor section viathe first compressor section bypass port and via the first compressorsection bypass valve to a bypass conduit; and directing the divertedfirst portion of the fluid through an auxiliary turbine positioned inthe bypass conduit wherein the first compressor section bypass controlvalve is positioned in the bypass conduit between the first compressorsection bypass port and the auxiliary turbine and wherein the secondcompressor section bypass control valve is positioned in the bypassconduit between the auxiliary turbine and the second compressor sectionbypass control port; opening the second compressor section bypasscontrol valve; opening a discharge control valve in fluid communicationwith the second compressor section bypass control valve and theauxiliary turbine; and diverting a second portion of the fluid flowingthrough the second compressor section via the second compressor sectionbypass port and via the second compressor section bypass control valveto the bypass conduit, directing a first portion of the diverted secondportion of the fluid through the auxiliary turbine positioned in thebypass conduit and directing a second portion of the diverted secondportion of the fluid through the discharge control valve.
 13. The methodof claim 12 further comprising: when the second compressor sectionbypass control valve is closed, discharging the diverted first portionof the fluid after flowing through the auxiliary turbine via a dischargeconduit and via the discharge control valve.
 14. The method of claim 12wherein a rotational speed of the auxiliary turbine is at least partlycontrolled by throttling said first compressor section bypass controlvalve.